EXPERIMENT STATION BULLETINS. 419 



TOBACCO DUST TREATMENT. - 



Tobacco dust, made by grinding tobacco stems into a fine powder, bas 

 proven quite efficient as an insecticide; so it was determined that it 

 should be given a trial. June 2, 1913, twenty-five pounds of tobacco dust 

 were spread over the surface of the soil in plot VII, and thoroughly 

 raked into the soil. The plot was then thoroughly soaked with water. 

 Later on in the day, lettuce and tomato seeds were planted in this plot. 

 June 30, 1913, the author dug up and examined some of the plants from 

 plot VII and found a few small knots on their roots. August 11, 1913, he 

 examined plants from plot VII and found knots on their roots. This 

 would seem to show that such an application of tobacco dust as was 

 used, would not eradicate this nematode. 



KEROSENE TREATMENT. 



August 11, 1913, all the plants from plot VI were dug up and the soil 

 then treated with commercial kerosene, using ten gallons on the seven by 

 ten foot plot. August 14, 1913,lettuce seed was planted in this plot. Septem- 

 ber 3, 1913, no plants had come up from the seed planted August 14th, so 

 the plot was replanted with lettuce. September 8, 1913, no plants were 

 up in this plot. No further data could be obtained on this treatment 

 during the fall, so no conclusions could be drawn at that time. Plants 

 from this plot were examined during the summer of 1914 and root-knots 

 M^ere found on them. 



GASOLINE TREATMENT. 



August 11, 1913, the writer dug up and removed the rest of the plants 

 from plot VII. The plot was then divided by setting a sheet of galvanized 

 iron thirty-six inches wide, into the soil eighteen inches. This gave two 

 plots five by seven feet in area. One of the plots was treated with com- 

 mercial gasoline, by sprinkling one gallon over the surface of the soil. 

 The other plot was treated in a similar manner except that three gallons 

 of gasoline were used instead of one. August 14, 1913, lettuce seed was 

 planted in both plots. September 8, 1913, the writer dug up and examined 

 lettuce plants from both of the gasoline treated plots and found many 

 knots on their roots. The heavy gasoline treatment appeared to have no 

 advantage over the light treatment, and neither seemed to inhibit the de- 

 velopment of the nematodes seriously. 



SUMMARY OP THE RESULTS OP THE FIELD TREATMENTS. 



In all of the foregoing experiments the knots found on the roots of 

 plants grown in the treated soils, were examined and dissected under a 

 microscope to make sure of their true cause. In each case where com- 

 plete data were obtainable they pointed to the conclusion that the treat- 

 ment used could not be depended upon to eradicate the root-knot nema- 

 todes from the treated soil. In some cases the treatment succeeded in 

 materially reducing the number of nematodes present in the soil, as 

 shown by the longer periods that the plants grew in some plots before 

 showing any knots on the roots. Treatments such as carbon bisulphide. 

 tobacco stems or strong formaldehyde solution, which greatly reduce the 

 number of nematodes in the soil for a month or so, might be of practical 



